Method for continuous drawing of wire rod

ABSTRACT

A wire rod is payed out from a pay-off stand and descaled in a descaling process. After preheating to a predetermined temperature by a preheating device, it is subjected to a lubrication pretreatment through a zinc calcium phosphate solution applied with ultrasonic wave in the lubrication pretreatment process. After rinsing process, the lubrication-pretreated wire rod is coated with a calcium stearate or a sodium stearate in lubricating process. Thereafter, the wire rod is dried sufficiently in drying process, and then added with a predies lubricant in wire drawing process and coiled by a coiler.

This application is a continuation of application Ser. No. 733,794,filed May 14, 1985 abandoned.

The present invention relates to a method for continuous drawing of awire rod for cold-forging, in which the wire rod (inclusive of a steelbar) is descaled, pretreated for lubrication, lubricated and drawn intowire while being moved continuously.

Secondary working for a wire rod for cold-forging is performed normallyin the order: descaling (pickling)--lubricationpretreatment--lubrication--drying--wire drawing--coiling. Among them,pickling, lubrication pretreatment and lubrication are usually renderedin batch treatment system. That is, heretofore, a pickled wire rod coilwas dipped in a phosphate solution of, for example, zinc phosphate and,thereafter, dipped in a lubricate solution of, for example, sodiumstearate to form a lubricate coating of such materials as sodiumstearate, zinc stearate, or zinc phosphate on the surface of the wirerod. The batch treatment system was heretofore used for the reason thata long period of reaction was required to obtain a coating having athickness sufficient to provide satisfactory lubricating properties,this required a longer treatment time and made an in-line systemdifficult.

Therefore, in, for example, Japanese Patent Public Disclosure No.163047/1981 Official Gazette, there is proposed a method for performinglubrication pretreatment and lubrication in an in-line system to therebyreduce equipment cost and improve productivity. This prior art methodhas been put into practical use. This prior art method is characterizedin that, after descaling, a wire rod is coated with zinc phosphate(lubrication pretreatment), further coated thereon with calcium stearateat room temperature (lubrication), and then rapidly dried. In this priorart method, it is made possible to reduce running cost, to coat arequired quantity of lubricant in a very short time, to dry it in ashort time, and to make it in an in-line system without extending theentire line unduly.

According to prior art methods, however, any of the batch treatmentsystem or the in-line system used zinc phosphate solution as thelubrication pretreatment, and therefore, had a disadvantage that thelubricant coating had unsatisfactory resistance to heat.

Generally in metal wire drawing operation, as described above, lubricantis indispensable to improve the working efficiency, to prolong the toollife, and to maintain the surface quality of drawn wire.

The lubricant for wire drawing reduces the friction between the dies andthe wire rod to thereby make it possible to draw the wire rod with asmaller drawing force and prevents wear of the dies. In addition tothese functions, the lubricant has important advantage that it remainssecurely as a coating on the surface of the wire after drawing and actsas an effective lubricant during cold forming (for example, boltmaking).

Heretofore, a predies lubricant having metallic soap as the maincomponent as follows was normally used in drawing wire:

    ______________________________________                                        metallic soap:     60-80% (by weight)                                         inorganic material:                                                                              20-40% (by weight)                                         additives:         several % (by weight)                                      ______________________________________                                    

In the prior art lubricant for wire drawing having metallic soap as themain component in which the metallic soap displays the basic lubricatingproperties, stearate or palmitinate of alkali earth metals or sodiumwere normally used. The typical inorganic material used in the prior artwire drawing lubricant is lime which prevents temperature rise in heavyworking to thereby prevent adhesion between the wire rod and the diesand to control the softening temperature of the lubricant. The additivesused in the prior art were one or more of sulfur, molybdenum disulfideand graphite which were added to prevent adhesion between the wire rodand dies under severe wire drawing conditions and to improve thelubricating properties.

However, while the prior art wire drawing lubricant having metallic soapas the main component had better properties than other wet typelubricants, it was still insufficient in the lubricating properties suchas resistance to heat produced in drawing and adhesiveness of thelubricant coating formed, which made the life of the wire drawing diesand the life of the dies for cold-forging subsequent to drawingrelatively short.

The drawn wire rods are mostly cold-forged into products. However, ithas become a recent trend that the lubricant used in the wire drawing isleft adhering onto the surface of the wire brought to the cold-forgingprocess so that the wire can be cold-forged into products without addingany lubricant. Therefore, while much better adhesiveness after wiredrawing and higher heat-resistance sufficient to prevent cracking in theadhering lubricant coating after wire drawing have been demanded for thelubricant for wire drawing, no successful lubricant for wire drawingwhich satisfactorily answer to these demands has been found yet.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for continuousdrawing of wire rod, in which the wire rod is descaled, pretreated forlubrication, lubricated, dried and drawn into wire in an in-line systemto thereby make it possible to obtain a lubricant coating highlyresistant to heat and to carry out the wire drawing operationefficiently in a shorter period of time than prior art methods.

Another object of the present invention is to provide a lubricant forwire drawing, which is capable of overcoming the above-describedproblems of the prior art lubricants and has highly desirable propertiessuch as reduction in friction, resistance to heat, and deposition andadherence to the wire rod, to thereby prolong the life of the dies forwire drawing and cold-forging.

The continuous wire drawing method according to the present invention ischaracterized in that a descaled and preheated wire rod is pretreatedfor lubrication by passing it through a calcium zinc phosphate solution(Ca/Zn=0.3-1.0) maintained in the temperature range 70° C.-90° C. andadded with an ultrasonic wave (frequency: 10-60 KHZ, output: 25 W/1liter solution), rinsed, lubricated by causing calcium stearate toadhere to it at room temperature or passing it through a sodium stearatesolution maintained in the temperature range 70° C.-90° C., dried andthen drawn into wire. Further, in said wire drawing operation, thepredies lubricant having metallic soap as the main component added with1-10 weight % of a thermoplastic resin (for example, Teflon,polyethylene, nylon, acrylic resin, polycarbonate) is used.

We have discovered that in wire drawing operation addition of athermoplastic resin to the prior art predies lubricant having metallicsoap as the main component improves the lubricating properties of thelubricant considerably. That is, by adding 1-10% by weight of athermoplastic resin to the prior art predies lubricant having metallicsoap as the main component, the lubricating properties of the lubricant,such as reduction of friction and resistance to heat, can be greatlyimproved.

Addition of the thermoplastic resin in less than 1% by weight isinsufficient to improve the lubricating properties satisfactorily. Onthe other hand, addition of it in more than 10% by weight increases thecost unduly and may result in generation of thermally decomposing gasesduring heat treatment after cold-forging. Particularly when any offluorine-contained polymers is used, addition of it in a percentagehigher than specified above is accompanied by the risk of generation offluoric gas during heat treatment after cold-forging. Accordingly, greatcare must be taken in determination of the percentage of addition of thethermoplastic resin.

The term "metallic soap" as used herein is to be understood to meanmetallic salts other than alkali salt, of, such as, fatty acid, resinacid and naphthenic acid, inclusive of sodium salt of these acids andtheir mixtures, preferably of common composition (commonly used as wiredrawing lubricant) containing calcium stearate or sodium stearate in 90%or more in weight added with one or more of aluminum stearate, zincstearate and barium stearate in several percent by weight.

Further, the term "a predies lubricant having metallic soap as the maincomponent" as used herein is to be understood to mean any of lubricantscontaining said metallic soap in 60% or more by weight, inorganicmaterial (such as lime) in 20% or more by weight, and several percent ofadditives (one or more of sulfur, molybdenum disulfide and graphite),that is, this term is applicable to any of known wire drawinglubricants.

The term "thermoplastic resin" as used herein is to be understood toapply to any of polyethylene resin, polypropylene resin,fluorine-contained polymers known as Teflon (trademark), polystyreneresin, vinyl acetal resin, polyacrylate resin, polymethacrylate resin,polyvinyl chloride resin, polyvinylidene chloride resin,polyacrylonitrile resin, polyvinylether resin, polyvinylketone resin,polyether resin, polycarbonate resin, thermoplastic polyester resin,polyamide resin, diene resin, polyurethane resin, and silicone resin.These resins are used solely or in combination of two or more kinds ofthem.

The thermoplastic resin is added preferably in the form of powder of thesize approximately of 10-20 μm diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings in which:

FIG. 1 is a block diagram of the process of the method for continuousdrawing of wire rod according to the present invention;

FIG. 2 is a graph showing the effect of application of an ultrasonicwave to lubrication pretreatment in the present invention;

FIG. 3 is a graph showing the relationship between the frequency of theultrasonic wave and the zinc calcium phosphate coating weight;

FIG. 4 is a graph showing the relationship between Ca/Zn ratio of thecalcium zinc phosphate coating and the zinc calcium phosphate coatingweight;

FIG. 5 is a graph showing the relationship between the concentration ofcalcium stearate and the calcium stearate coating weight;

FIG. 6 is a graph showing the relationship between the treating time ofthe sodium stearate and the zinc stearate coating weight;

FIG. 7 is a schematic side view of an apparatus for ultrasonicpretreatment for lubrication;

FIG. 8 is a schematic front view of a treating bath;

FIG. 9 is a graph showing the relationship between the quantity ofethylene tetrafluoride resin added to the predies lubricant havingmetallic soap as the main component and the drawing force in the wiredrawing operation using the lubricant;

FIG. 10 is a graph showing the adhesiveness of the lubricant coating inthe cold-forging process;

FIG. 11a is a schematic view of the shape of the cut wire rod beforecold-forging;

FIG. 11b is a schematic view of the shape of the product of thecold-forging;

FIG. 12 is a graph showing comparatively the results of Bowden tests ofthe materials subjected to wire drawing and cold-forging using thelubricant according to the present invention and the conventionallubricant, respectively; and

FIG. 13 is a graph showing the results of Bowden tests of the materialin an example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawings and more particularly to FIG. 1thereof, there is shown in block diagram treating processes of themethod according to the present invention. As shown, a wire bar is payedout from a pay-off stand 1 and descaled in descaling process 2 by, forexample, shot blasting. Subsequently, the wire rod is preheated by apreheating device 3 to a predetermined temperature (80° C. or higher)and then pretreated for lubrication in lubrication pretreatment process4 by passing it through a calcium zinc phosphate solution(Ca/Zn=0.3-1.0) added with an ultrasonic wave. The calcium zincphosphate solution is preheated to the temperature 70°-90° C. Then,after rinsing process 5, the pretreated wire rod is lubricated bycalcium stearate or sodium stearate to adhere thereto in lubricatingprocess 6. Lubrication by calcium stearate is carried out at roomtemperature. However, sodium stearate is to be preheated to 70°-90° C.for lubrication in process 6. After lubricated, the wire rod is driedsufficiently in its lubricant coating in drying process 7, drawn with apredies lubricant in wire drawing process 8, and coiled by coiler 9.

Method of descaling rod used in descaling process 2 is not limited. Anyof pickling, shot blasting and roll bending may be used to descale therod in process 2. Among the three methods mentioned above, shot blasingis most preferable for the phosphate coating in an in-line system.

The method according to the present invention is characterized in thatcalcium zinc phosphate (Ca/Zn=0.3-1.0) having a good resistance to heatis used in process 4 to pretreat the wire rod for lubrication. Thetemperature of removing crystal water of the calcium zinc phosphatecoating is 415° C. while the temperature of removing crystal water ofthe heretofore used zinc phosphate coating is 280°-290° C. This meansthat the prior art zinc phosphate coating is removed of its crystalwater by the heat (normally up to 300° C.) developed during wire drawingoperation to thereby cause cracks in the coating. In contrast to this,since the temperature of removing crystal water of the calcium zincphosphate coating according to the present invention is, as mentionedabove, as high as 415° C., no crack is caused in the coating by the wiredrawing operation.

The method according to the present invention is characterized in thatan ultrasonic wave is used in treatment to obtain a sufficient zinccalcium phosphate coating weight and to control the coating weight. Thisis because the calcium zinc phosphate solution is less sensitive tochemical conversion treatment than the zinc phosphate solution and ismore difficult to obtain the coating weight. However, as shown in FIG.2, the zinc calcium phosphate coating weight is increased by applicationof the ultrasonic wave thereto. The results shown in FIG. 2 wereobtained under the treatment conditions: concentration 160 points,temperature 80° C., and frequency of the ultrasonic wave 50 KHZ at 1 KW.

As shown in FIG. 3, the frequency of the ultrasonic wave applied to thesolution is preferably in the range 10-60 KHZ because the frequencylower than 10 KHZ presents a problem of noise and, on the other hand,the frequency higher than 60 KHZ is less effective to obtain asufficient coating weight. Output of the ultrasonic wave is preferably25 W per liter of the solution.

The Ca/Zn ratio of the calcium zinc phosphate coating is determined to0.3-1.0 for the reason described below. FIG. 4 shows the relationshipbetween the Ca/Zn ratio of the calcium zinc phosphate coating(concentration of the solution 160 points) and the coating weight. Asunderstood from FIG. 4, when the Ca/Zn ratio is lower than 0.3, effectof addition of Ca is small and the resistance to heat is not sufficient.On the other hand, when the Ca/Zn ratio is higher than 1.0, thesensitiveness to chemical conversion treatment is not sufficient and itis difficult to obtain a predetermined coating weights (≧6 g/m²) and ofmetallic soap (≧1 g/m²). Accordingly, the Ca/Zn ratio of the calciumzinc coating is preferably in the range 0.3-1.0.

The predetermined coating weight of the calcium zinc phosphate coatingweight of 6 g/m² or larger is obtained in a short period of time 10-20seconds only when the concentration of the calcium zinc phosphatesolution is 160 points or higher. On the other hand, the concentrationof the solution of 200 points or higher is not economical since thecoating weight in proportion to the increase in the concentration is notobtained. Here, the lower limit of the coating weight of the calciumzinc phosphate coating is predetermined to 6 g/m². The prior art zincphosphate coating having lower resistance to heat requires the coatingweight of the lower limit 7-8 g/m². However, since the calcium zincphosphate coating according to the present invention has a highresistance to heat, the coating weight of it can satisfactorily be aslow as 6 g/m².

The apparatus used for ultrasonic pretreatment for lubrication in themethod according to the present invention may take the construction inwhich, as shown in FIGS. 7 and 8, a plurality of ultrasonic waveapplying devices 12 are disposed vertically or horizontally in pairs inparallel or staggered positions on the outer peripheral surface of acylindrical treating bath 11, return pipes 14 are provided betweentreating solution receivers 13 projecting from the inlet side and theoutlet side, respectively, of the treating bath 11 and a treatingsolution tank 15 to collect treating solution 19 therethrough, and apump 16 is provided to supply the treating solution from the treatingsolution tank 15 to the treating bath 11 through piping 17. By theapparatus constructed as described above, the calcium zinc phosphatesolution is subjected to the ultrasonic wave and agitated, and caused torapidly adhere to the surface of a wire rod 18 by cavitation. Further,it is made possible to control the coating weight of the calcium zincphosphate solution by using or not using the application of theultrasonic wave or by changing the frequency or the output of theultrasonic wave applying device.

The lubrication process is carried out after the lubricationpretreatment process by passing the wire rod either (1) through calciumstearate solution at room temperature or (2) through sodium stearatesolution heated to the temperature 70°-90° C.

In lubrication with calcium stearate (1), as will be understood from therelationship between the concentration and the coating weight shown inFIG. 5, the concentration must be 300 g/liter or higher in order toobtain the predetermined coating weight of 5 g/m² or higher. While anyof wet spraying (coating solution) and dry spraying (coating powder) canbe used to cause calcium stearate to adhere to the wire rod, coating bywet spraying is preferred in view of the coating weight of the lubricantand the adhesiveness of the lubricant coating. Treating time of 2-3seconds is normally required for physical adhesion.

In lubrication with sodium stearate (2), batch treatment system can beused. In this lubrication with sodium stearate, substitution takes placebetween the calcium zinc phosphate coating formed by lubricationpretreatment and the sodium stearate solution to produce a zinc stearatelayer which adheres to the surface of the wire rod. In this lubrication,it is normally required to obtain the coating weight of the substitutionproduct layer of 1 g/m² or higher. For this purpose, as seen from therelationship between the treating time with sodium stearate and the zincstearate coating weight shown in FIG. 6, a period of time of 20 secondsor longer is required.

The lubrication (1) or (2) above may be omitted in the case where apredies lubricant is used during wire drawing process.

In the method according to the present invention, the predies lubricantis added to increase the heat-resistance and lubricating properties. Thepredies lubricant used in the method according to the present inventionis the lubricant having metallic soap as the main component added with athermoplastic resin such as Teflon, polyethylene, nylon, acrilic resin,and polycarbonate in 1-10% by weight. The thermoplastic resin is addedto the metallic soap lubricant to make use of the heat-resistance andthe low friction of the thermoplastic resin such, for example, asTeflon. Further, the quantity of addition of the thermoplastic resin isdetermined to 1-10% by weight because addition of it in less than 1% isnot sufficient to provide an effect to the drawing force and, on theother hand, while a larger quantity of addition of it provides a largereffect, the upper limit of the quantity of its addition is determined to10% considering the cost and the fact that the decomposition gas of, forexample, Teflon is fluorine gas.

FIG. 9 shows graphically the relationship between the quantity ofaddition of ethylene tetrafluoride (trademark "Teflon") to the wiredrawing lubricant containing metallic soap as the main component (havingthe content: calcium stearate 70%, lime 27%, and sulfur 3% by weight)and the drawing force required to draw a steel rod (equivalent to S45Cof JIS--Japanese Industrial Standard) into wire. The graph of FIG. 9shows the results of drawing of said steel rod coated with zincphosphate as the lubrication pretreatment and having the diameter 5.5mmφ into wires with two different reduction of area, approximately 20%and approximately 30%, respectively.

It is clear from FIG. 9 that the required drawing force shows thetendency to decrease suddenly when the quantity of addition of theethylene tetrafluoride containing resin exceeds 1% by weight. Thistendency has been confirmed to appear likewise when other thermoplasticresin is added. While the graph of FIG. 9 shows that the thermoplasticresin is added preferably in larger quantity from the view to increasethe lubrication, the quantity of its addition is required to be limitedto 10% by weight or less in view of the environmental pollution andeconomy as mentioned hereinabove.

FIG. 10 shows graphically the comparative results of the adhesiveness ofthe lubricant coating to the rod being worked between the predieslubricant with no resin added and the predies lubricant with athermoplastic resin added.

The wire drawing lubricant, the thermoplastic resin added and thelubrication pretreatment method used in the tests shown in FIG. 10 werethe same as those used in the tests of FIG. 9, and the wire rod used wasa boron steel equivalent to 10B22M of AISI. The coating weight wasmeasured in the manner described below.

A boron steel rod of the diameter 22 mmφ coated with zinc phosphate orzinc calcium phosphate (pretreatment for lubrication) was drawn into rodof 19.5 mmφ with the reduction of area of approximately 21.4% using bothof the predies lubricant added with no resin and the predies lubricantadded with ethylene tetrafluoride containing 3% by weight, and subjectedto cold-forging (extruding to make bolts) during which sampling isstarted to find the rate of residual lubricant on the drawn rod(extruding reduction of area=0) at each extruding reduction of area.That is, the adhesiveness of the lubricant coating is understood as thefollowing ratio: ##EQU1## The larger the value of the rate of residuallubricant coating is, the better the adhesiveness of the coating is orthe more the lubricant remains and, accordingly, the less frequently theseizure occurs during the cold-forging operation. In the cold-forgingused in the method according to the present invention, a rod (diameter:d₀) shown in FIG. 11a is formed to, as shown in FIG. 11b, a bolt-likeshape (diameter of shank: d₁) leaving a head undrawn, with the ratio ofmaximum accumulated reduction of area of approximately 80%. In thiscase, the ratio of reduction of area is given by the formula: ##EQU2##

It is understood from the results shown in FIG. 10 that the predieslubricant added with ethylene tetrafluoride containing 3% by weight isobviously superior in adhesiveness of the lubricant coating to thelubricant added with no resin. This shows that the addition of theethylene tetrafluoride increases the heat resistance of the lubricantand prevents its deterioration by heat generated during working.

FIG. 12 shows the results of Bowden tests (using a Bowden tester forrubbing the surface of the test piece by a steel ball to determine thecoefficient of friction corresponding to the number of sliding times)using extruded rods obtained by the cold-forging process described above(extrusion reduction of area: approximately 79.5%).

It is understood from FIG. 12 that the rod coated thereon with thepredies lubricant added with the ethylene tetrafluoride in 3% by weighthas obviously lower coefficient of friction than the rod coated thereonwith the predies lubricant added with no such resin and is lower in therise of the coefficient of friction than it. Therefore, FIG. 12 showsthat the predies lubricant added with the thermoplastic resin issuperior in lubricating properties and adhesiveness of its coating.

EXAMPLE

By the equipment having the line construction shown in FIG. 1, usingshot blasting for descaling of the wire rod, and including theultrasonic pretreatment apparatus for lubrication shown in FIGS. 7 and8, a material of 5.5 mmφ (S45C) was drawn in the following operativeconditions into rods of 4.95 mmφ and 4.6 mmφ, respectively:

Operating Conditions

(1) Descaling Condition

Shot blasting Material: steel balls 0.3 mmφ

Shot Density: approximately 300 Kg/m²

(2) Preheating Condition

Steam Blowing: at temperature of 80° C.

(3) Lubrication Pretreatment Condition

Lubrication Pretreating Agent: calcium zinc phosphate solution(Ca/Zn=0.5)

Treatment Condition: 160 points (concentration )×80° C. (temperature)×15sec. (reaction time), ultrasonic wave: 50 KHZ, 1 KW

(4) Lubricating Condition

(i) When using calcium stearate

Concentration: 300 g/liter

Temperature: room temperature

Time: 3 seconds

(ii) When using sodium stearate

Concentration: 90 g/liter

Temperature: 80° C.

Time: 25 seconds

(5) Drying Condition

Infrared Drying Furnace: furnace temperature 80° C.

(6) Wire Drawing Condition

Predies Lubricant: lubricant having calcium stearate as the maincomponent added with Teflon in 3%

Reduction of Area:

approximately 19% (5.5 mmφ→4.59 mmφ)

approximately 30% (5.5 mmφ→4.6 mmφ)

Wire Drawing Speed: 80 m/mm

Table 1 shows the drawing force in the method according to the presentinvention in comparison with prior art method (Lubrication Pretreatment:zinc phosphate, Predies Lubrication: only a lubricant on the markethaving calcium stearate as the main component).

                  TABLE 1                                                         ______________________________________                                        Drawing Force                                                                                Ratio of Drawing Reduc-                                                       tion of Area (%)                                                                5.5.sup.φ  → 4.95.sup.φ                                                    5.5.sup.φ  → 4.6.sup.φ            Lubricating Condition                                                                          (approx. 19%)                                                                             (approx. 30%)                                    ______________________________________                                        Present Invention                                                             1    calcium zinc phosphating                                                                      785 Kg.     970 Kg                                            -- predies lubrication                                                        added with Teflon                                                        2    calcium zinc phosphating                                                                      770 Kg      950 Kg                                            -- calcium stearate +                                                         predies lubrication                                                           added with Teflon                                                        3    calcium zinc phosphating                                                                      730 Kg      910 Kg                                            -- sodium stearate +                                                          predies lubrication                                                           added with Teflon                                                        Prior                                                                              zinc phosphating --                                                                           822.5 Kg    1032.5 Kg.                                   Art  calcium stearate predies                                                      lubrication                                                              ______________________________________                                    

FIG. 10 shows the results of Bowden tests (lubricating properties andadhesiveness of the lubricant coating) of the rod after winding. Table 2shows the number of sliding times when μ=0.2 in comparison between themethod according to the present invention and the prior art method.

                  TABLE 2                                                         ______________________________________                                        Bowden Sliding Times (μ = 0.2)                                                          Ratio of Reduction of Area                                                    5.5.sup.φ  → 4.95.sup.φ                                                 5.5.sup.φ  → 4.6.sup.φ                   ______________________________________                                        Present  1         300        215                                             Invention                                                                              2         330        240                                                      3         365        270                                             Prior Art       92         74                                                 ______________________________________                                    

Table 3 shows the life of each of the wire drawing dies and thecold-forging dies used for drawing rods under the conditions describedabove (provided, the drawing reduction of area: 5.5φ→4.95φ) and thencold-forging them into high tension bolt in comparison with such life inthe prior art.

                  TABLE 3                                                         ______________________________________                                        Life of Wire Drawing and Cold-Forging Dies                                              Wire Drawing Dies                                                                         Cold-Forging Dies                                       ______________________________________                                        Present Invention                                                                         50 tons       800 tons                                            Prior Art   10 tons       240 tons                                            ______________________________________                                         Life is expressed by tons of products before replacement of the dies for      wear or damage thereof.                                                  

As will be seen from Tables 1 and 2 and FIG. 13, the lubricant coatingaccording to the present invention is superior in heat resistance andadhesiveness to the zinc phosphate coating according to the prior art.Accordingly, the life of the drawing and the cold forging dies isconsiderably prolonged in the method according to the present invention.

In the method according to the present invention, as describedhereinabove, since calcium zinc phosphate is used as the lubricationpretreating agent, it is made possible to obtain a coating having ahigher temperature of removing crystal water and a higher heatresistance than the zinc phosphate coating according to the prior art,and since an ultrasonic wave applying device is used, it is madepossible to secure and control freely coating weight of the calcium zincphosphate coating. Further, since the lubricant pretreated rod islubricated by calcium stearate or dodium stearate, the lubricatingproperties as well as the heat resistance can be improved. Moreover,since a prior art lubricant having metallic soap as the main componentadded with a thermoplastic resin such as Teflon is used as the predieslubricant during wire drawing operation, it is made possible to improvethe heat resistance and the lubricating properties of the lubricantcoating and to prolong considerably the life of the cold-working tools.

While we have described and illustrated a present preferred method ofpracticing the invention, it is to be distinctly understood that theinvention is not limited thereto but may be otherwise variouslypracticed within the scope of the following claims.

What is claimed is:
 1. A method for continuously drawing a wire rod intoa wire, comprising the steps of:descaling the wire rod; preheating thedescaled wire rod; pretreating the preheated wire rod for lubrication bypassing said rod through a calcium zinc phosphate solution heated to70°-90° C. and having the ratio (Ca/Zn)=0.3-1.0; rinsing the pretreatedwire rod; lubricating the rinsed wire rod by coating said rod with acalcium stearate or a sodium stearate; drying the lubricated wire rod;lubricating the dried wire by coating said wire with a predies lubricanthaving metallic soap as the main component added with an ethylenetetrafluoride in 1-10% by weight; and drawing the dried wire rod into awire.
 2. A method according to claim 1, characterized in that anultrasonic wave is applied to said calcium zinc phosphate solution insaid process of pretreatment for lubrication.
 3. A method according toclaim 1, characterized in that the ultrasonic wave applied to saidcalcium zinc phosphate solution has the frequency of 10-60 KHZ and theoutput of 25 W/1 liter solution.
 4. A method according to claim 1,characterized in that, in said lubricating process, said pretreated wirerod is coated with a calcium stearate at room temperature.
 5. A methodaccording to claim 1, characterized in that said pretreated wire rod ispassed through a sodium stearate solution heated to 70°-90° C. to coatit with said solution.
 6. A method according to claim 1, characterizedin that, in said process for drawing wire after drying, a wire drawinglubricant having metallic soap as the main component added with athermoplastic resin in 1-10% by weight is used as the predies lubricant.7. A method according to claim 1, characterized in that said calciumzinc phosphate solution has the ratio (Ca/Zn)=0.3-0.5.